This invention relates to a tilt locking system for ship propellers and more particularly to an improved arrangement for controlling the tilting movement of a marine outboard drive.
As is well known, it is the normal practice to mount a marine outboard drive for pivotal movement about a horizontally disposed tilt axis so that the propeller can be tilted up out of the water when not in use. The term "marine outboard drive" is used herein generically to cover both outboard motors and the outboard drive unit of a marine inboard/outboard drive. When the lower end of the outboard drive strikes an underwater obstacle, it is desirable to permit the motor to tilt or pop up so as to clear this obstacle. However, the tilting mechanism should insure that the outboard drive returns to its normal position once the obstacle is cleared and also that the outboard drive is held against such movement under normal acceleration and driving forces both in forward and reverse.
It has been proposed to employ a hydraulic cylinder assembly with appropriate valving and controls for achieving some of these results. Such an arrangement is shown in copending application Ser. No. 326,553, filed Dec. 2, 1981, now U.S. Pat. No. 4,493,659 entitled "Tilt Lock Mechanism", filed in the name of Takashi Iwashita, and assigned to the assignee of this application. In that application, several embodiments of tilt locking systems for outboard drives are shown. In each embodiment, a hydraulic piston and cylinder assembly is interposed between the drive member of the outboard drive and the hull to which the outboard drive is pivotally attached. The piston divides the cylinder into first and second chambers and flow between these chambers is permitted by valved passages so that the motor may tilt up when striking an obstacle and will return to its normal state once the obstacle is passed. Tilting up action when an underwater obstruction is encountered is accomplished by means of a passage that permits flow between the respective chambers of the hydraulic unit and which includes a pressure responsive absorber valve to permit the outboard drive to tilt up when a predetermined force is exerted to it. The outboard drive is permitted to move downwardly by means of a second passage that includes a pressure responsive relief valve for permitting the flow back from the one chamber to the other when the obstacle is no longer encountered.
In order to facilitate manual tilting up of the outboard drive, a bypass passage having a manually controlled valve is provided. This valve may be opened to permit free movement of the fluid between the two chambers to facilitate tilting up of the outboard drive.
In some instances, it is desirable to raise the engine only slightly so as to adjust its trim position. An example of when this is done is when operating in shallow water. Under these conditions, the outboard drive is operated at a shallower angle so as to prevent it from contacting the bottom. However, the weight of the motor will cause the relief valve will open when the motor is tilted up and permit the motor to swing back to its normal operating condition.
It is, therefore, a principal object of this invention to provide an improved tilt locking and shock absorbing arrangement for a marine outboard drive.
It is another object of the invention to provide a tilt locking and shock absorbing construction for a marine outboard drive that permits the motor to be tilted up without interference from the shock absorbing unit.
It is a further object of the invention to provide a tilt locking and shock absorbing arrangement for an outboard motor that permits the motor to be adjusted for trim without having the motor gradually returned to the normal condition.